Layered structure for use with high power light emitting diode systems

ABSTRACT

A layered structure for use with a high power light emitting diode system comprises an electrically insulating intermediate layer interconnecting a top layer and a bottom layer. The top layer, the intermediate layer, and the bottom layer form an at least semi-flexible elongate member having a longitudinal axis and a plurality of positions spaced along the longitudinal axis. The at least semi-flexible elongate member is bendable laterally proximate the plurality of positions spaced along the longitudinal axis to a radius of at least 6 inches, twistable relative to its longitudinal axis up to 10 degrees per inch, and bendable to conform to localized heat sink surface flatness variations having a radius of at least 1 inch. The top layer is pre-populated with electrical components for high wattage, the electrical components including at least one high wattage light emitting diode at least 1.0 Watt per 0.8 inch squared.

This application is a continuation of U.S. application Ser. No. 13/411,322, filed Mar. 2, 2012, which is a continuation of U.S. applicationSer. No. 12/043,424, filed Mar. 6, 2008, now U.S. Pat. No. 8,143,631,issued Mar. 27, 2012, the contents of which are herein incorporated byreference.

FIELD OF THE INVENTION

The present invention relates to a layered structure for use with highpower light emitting diode systems.

BACKGROUND OF THE INVENTION

Lighting systems utilizing multiple emitters or light emitting diodes(hereinafter “LEDs”) are used in a variety of applications including butnot limited to retail displays, refrigeration and freezer door systems,under cabinet lighting, track lighting, and cove lighting. Continuousstrings of LEDs are often used in these applications and may beindividually wired together or soldered onto printed circuit boardsubstrates. Typical applications use standard circuit board materialssuch as Flame Retardant 4 (hereinafter “FR4”) or Metal Core PrintedCircuit Boards (hereinafter “MCPCBs”), which are typically rigid.

Designers of high power LED systems quickly adopted these standardcircuit board materials due to their low cost and wide spreadavailability. The broadest applications focus on the use of aluminumclad MCPCBs in an attempt to transfer the high amount of heat generatedfrom high power LEDs (1 W or higher). FR4 materials are known to be poorthermal solutions for high heat circuits as the electrically insulatinglayer results in poor thermal conductivity from the LED heat sink slugto the assembly heat sink. Thus, LED manufacturers typically recommendMCPCBs in place of FR4 for use in high power LED applications, such asPhilips Lumileds Lighting Company in its Custom LUXEON® Design Guide,Application Brief AB12 (3/06).

Standard circuit board materials are typically rigid material in formand do not conform to irregularities in heat sink surfaces. The standardcircuit board materials are commonly screwed onto metal heat sinks withthermal grease placed between the aluminum clad and the assembly heatsink with some applications using thermal tape in place of mechanicalfastening and thermal grease. Thermal grease and adhesive thermal tapesfill small voids of 0.002 inch or less due to surface irregularities butare not sufficient to fill larger voids or air gaps commonly occurringbetween standard circuit board materials and the assembly heat sinks dueto the heat sinks being made out of flat, twisted, or curved surfaces.Issues with poor conductive interfaces quickly lead to failed LEDsystems in applications in the field due to voids or air gaps betweenthe MCPCB or other substrate and the intended heat sink. Theseapplications typically suffer from poor transfer of heat from the LEDsource to the heat sink due to poor conductive surface contact due tothe board being too rigid to conform to the heat sink shape or to poorheat transfer through the board due to MCPCB thickness and layeredstructure properties.

More exotic solutions are available for LED systems including metal cladboards with thin, higher thermal conduction insulating layers or printedceramic circuits onto steel or aluminum substrates. These materialsprovide better thermal management of high power LEDs over standardcircuit board materials due to their higher thermally conductivematerials but suffer from the same heat sink interface issues as thestandard circuit board material and further at a severe sacrifice tosystem costs. Printed circuit board materials, such as T-lam™. ThermallyConductive Printed Circuit Board Materials by Laird Technologies, areone example of the more exotic, costly materials used to increase thethermal conductivity through the electrical insulating part of thestructure.

LED systems are sought as energy efficient solutions to replace manyestablished, less efficient lighting systems using common lightingsources such as incandescent, halogen, and fluorescent lighting sources.The introduction of LED systems into many general illumination anddisplay applications is limited due to the high front end costs of LEDsystems. While the performance of the LEDs continue to climb and thecost of the LEDs continues to drop at rates consistent with othersemiconductors following Mohr's Law, little is being done to reduce thecosts related to the support systems necessary for high power LEDsystems such as board substrates.

The costs of assembling LED systems into lighting fixtures are furtherincreased due to the labor intensive nature of applying rigid boardmaterials with thermal grease, paste, or adhesive along with mechanicalfastening of the rigid board materials to heat sinks. Flexible tape andreel solutions have been developed for low wattage LED systems, however,these solutions are not applicable to high wattage LED systems due tothe amount of heat generated by the higher wattage systems and theinherent poor thermal properties of the flexible materials such asDuPont™ Kapton™ polyimide film.

Therefore, there exists a need for a cost effective, high thermalperformance substrate or solution for use with high power LED systems.The present invention addresses the problems associated with the priorart devices.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a layered structure for usewith a high power light emitting diode system comprising an electricallyinsulating intermediate layer interconnecting a top layer and a bottomlayer. The top layer, the intermediate layer, and the bottom layer forman at least semi-flexible elongate member having a longitudinal axis anda plurality of positions spaced along the longitudinal axis. The atleast semi-flexible elongate member is bendable laterally proximate theplurality of positions spaced along the longitudinal axis to a radius ofat least 6 inches, twistable relative to its longitudinal axis up to 10degrees per inch, and bendable to conform to localized heat sink surfaceflatness variations having a radius of at least 1 inch. The top layer ispre-populated with electrical components for high wattage, theelectrical components including at least one high wattage light emittingdiode at least 1.0 Watt per 0.8 inch squared.

Another aspect of the present invention provides a layered structure foruse with a high power light emitting diode system comprising a toplayer, a bottom layer, an electrically insulating intermediate layer,and a thermally conductive adhesive layer. The top layer includes 0.5 to4.0 ounces per square foot of copper having first electrical circuitsand protective coating, and the top layer is configured and arranged toreceive at least one high wattage light emitting diode at least 1.0 Wattper 0.8 inch squared. The bottom layer includes 0.5 to 4.0 ounces persquare foot of copper having second electrical circuits. Theelectrically insulating intermediate layer includes fiberglass 0.005 to0.020 inch thick, and the intermediate layer interconnects the top layerand the bottom layer. The thermally conductive adhesive layer isoperatively connected to the bottom layer on an opposing side to theintermediate layer. The top, intermediate, bottom, and adhesive layershave a thermal resistance of less than 1 to 5 degrees Celsius per Watt.

Another aspect of the present invention provides a method of making alayered structure. A first layer made of a first electrically conductivematerial, a second layer made of a second electrically conductivematerial, and an intermediate layer made of an electrically insulatingthermally conductive material are obtained. The intermediate layer issandwiched between the first layer and the second layer. A firstelectrical circuit is placed on a top surface of the first layer, and aportion of the top surface is coated with a protective coating. A secondelectrical circuit is placed on a bottom surface of the second layer. Aplurality of high wattage electrical components are connected to thefirst electrical circuit, the high wattage electrical componentsincluding at least one high wattage light emitting diode at least 1.0Watt per 0.8 inch squared.

Another aspect of the present invention provides a method of connectinga layered structure to a heat sink. The layered structure includes anelectrically insulating intermediate layer interconnecting a top layerand a bottom layer. A thermally conductive adhesive layer is connectedto the bottom layer and includes a removable backing. The top layer, theintermediate layer, the bottom layer, and the adhesive layer form an atleast semi-flexible elongate member having a longitudinal axis and aplurality of positions spaced along the longitudinal axis. The at leastsemi-flexible elongate member is bendable laterally proximate theplurality of positions spaced along the longitudinal axis to a radius ofat least 6 inches, twistable relative to its longitudinal axis up to 10degrees per inch, and bendable to conform to localized heat sink surfaceflatness variations having a radius of at least 1 inch. The top layer ispre-populated with electrical components for high wattage, theelectrical components including at least one high wattage light emittingdiode at least 1.0 Watt per 0.8 inch squared. A desired length of thelayered structure is determined, and the layered structure is cut intothe desired length. The backing is removed from the adhesive layer ofthe desired length. The desired length is placed on a heat sink,pressure is applied on the desired length, and a termination board isconnected to the desired length.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a layered structure for use with highpower light emitting diode systems constructed according to theprinciples of the present invention with a plurality of light emittingdiodes operatively connected thereto;

FIG.2 is a cross-section view of the layered structure shown in FIG. 1;

FIG. 3 is a top view of the layered structure shown in FIG. 1 with athermally conductive top layer circuit printed thereon;

FIG. 4 is a bottom view of the layered structure shown in FIG. 1;

FIG. 5 is a top view of the layered structure shown in FIG. 1operatively connected to a first heat sink;

FIG. 6 is a side view of the layered structure operatively connected tothe first heat sink shown in FIG. 5;

FIG. 7 is a top view of the layered structure shown in FIG. 1operatively connected to a second heat sink;

FIG. 8 is a perspective view of the layered structure operativelyconnected to the second heat sink shown in FIG. 7;

FIG. 9 is an exploded perspective view of the layered structure shown inFIG. 1 operatively connected to a third heat sink;

FIG. 10 is an exploded perspective view of the layered structure shownin FIG. 1 operatively connected to a fourth heat sink;

FIG. 11 is a side view of a reel onto which the layered structure shownin FIG. 1 could be wound;

FIG. 12 is a top schematic view of the layered structure shown in FIG.1;

FIG. 13 is a side schematic view of the layered structure shown in FIG.12;

FIG. 14 is a top schematic view of the layered structure shown in FIG.12 with a twist relative to its longitudinal axis; and

FIG. 15 is a top view of a “peel and stick” layered structure for usewith high power light emitting diode systems constructed according tothe principles of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A preferred embodiment layered structure for use with high power lightemitting diode systems constructed according to the principles of thepresent invention is designated by the numeral 100 in the drawings.

As shown in FIG.2, the layered structure 100 generally includes a toplayer 101, an intermediate layer 110, and a bottom layer 112.Preferably, a commercially available FR4 material is used as a startingmaterial and is modified to create the layered structure 100. The FR4material preferably includes a layer of fiberglass sandwiched betweentwo layers of copper. An example of a suitable FR4 material is FR406manufactured by Isola Group of Chandler, Ariz. The top layer 101includes one of the two layers of copper, the intermediate layer 110includes the layer of fiberglass, and the bottom layer 112 includes theother of the two layers of copper. It is recognized that other suitableFR4 materials could be used and that these layers could be eithermanufactured or purchased in this form.

Prior to modification, the top layer 101 is preferably copperapproximately 0.5 to 4.0 ounces per square foot and is approximately0.0007 to 0.0056 inch thick, 0.25 to 18.00 inches wide, and 0.50 to24.00 inches long. Although copper is the preferred material, it isrecognized that other suitable electrically conductive materials such asbut not limited to aluminum could be used. The top, copper layer ispreferably modified to include a thermally conductive printed or etchedelectrical circuit 103 using standard electrical circuit design toolsand techniques well known in the art and is then coated with aprotective coating using standard solder masking and labeling techniqueswell known in the art. An example of a suitable protective coating thatcould be used is TechniMask ISR 1000 manufactured by Technic, Inc. ofCranston, R.I.

The top layer 101 is designed in such a way as to provide receptaclesand mounting surfaces for LEDs 125 and other SMT electrical componentsproximate the top surface 102. The top surface 102 of the top layer 101is shown in FIG. 3. The top layer 101 includes a plurality of LEDreceptacles 104 to which LEDs are operatively connected, driverlocations 107, and jumper locations 108. The printed circuit 103, theLED receptacles 104, the driver locations 107, and the jumper locations108 are preferably made of copper 105 and receive a hassel coating.

The intermediate layer 110 is not modified and is an electricallyinsulating thermally conductive layer preferably made of fiberglassapproximately 0.005 to 0.020 inch thick, 0.25 to 18.00 inches wide, and0.50 to 24.00 inches long. The fiberglass has a breakdown voltage ofgreater than 50 kilovolts (kV), a tensile strength of 55 kips per squareinch (ksi), and a flexural strength of 91 kips per square inch (ksi).The thermal conductivity of the fiberglass is preferably 0.3 to 0.4Watts per meter per degrees Kelvin (W/mK). Although fiberglass is thepreferred material, it is recognized that other suitable materials suchas but not limited to polymer or ceramic blended dielectrics may beused.

Prior to modification, the bottom layer 112 is preferably copperapproximately 0.5 to 4.0 ounces per square foot and is approximately0.0007 to 0.0056 inch thick, 0.25 to 18.00 inches wide, and 0.50 to24.00 inches long. Although copper is the preferred material, it isrecognized that other suitable electrically conductive materials such asbut not limited to aluminum could be used. The bottom, copper layer ispreferably modified into a heat spreading copper circuit laterally andalong its longitudinal axis proximate the bottom surface using standardelectrical circuit design tools and techniques well known in the art inorder to rapidly spread the heat through the bottom layer 112. Theexposed copper proximate the bottom surface of the bottom layer 112 isthen tinned. The bottom surface of the bottom layer 112 is shown in FIG.4. The bottom layer 112 includes thermally conductive printed circuits,which are printed or etched using solder mask printing, photo etching,and solder masking techniques well known in the art for producingelectrical circuits.

Optionally, the layered structure 100 may also include an adhesive layer114. The adhesive layer 114 is preferably a two-sided thermallyconductive tape with two removable layers of protective backing. One ofthe removable layers of protective backing is removed to expose one sideof the adhesive, which is then operatively connected to the bottomsurface of the bottom layer 112. When it is later desired to operativelyconnect the layered structure 100 to a heat sink, the second removablelayer of protective backing 115 is removed to expose the other side ofthe adhesive. The adhesive layer 114 provides thermal contact betweenthe layered structure 100 and the heat sink and is capable of fillingvoids and air gaps approximately 0.002 inch or less.

An example of a suitable adhesive layer is 3M™. Thermally ConductiveAdhesive Transfer Tape 8810. Although a two-sided thermally conductivetape is preferably used, it is recognized that other suitable thermallyconductive connecting materials could be used.

The layered structure 100 is preferably an integral, layered structurethat is at least semi-flexible, not rigid. Preferably, the layeredstructure 100, including the optional adhesive layer 114, is anelongate, at least semi-flexible, strip with a thickness ofapproximately 0.020 to 0.50 inch, a width of approximately 0.25 to 18.00inches, and a length of any desired length, which could be as long as250 feet or more. As shown in FIG. 12, the semi-flexible layeredstructure 100 has a longitudinal axis L.sub.1 . In this at leastsemi-flexible form, the strip can bend laterally, as shown in FIG. 13,along a plurality of positions L.sub.2 (only one shown) spaced along thelength of the longitudinal axis L.sub.1 to a radius of 6 inches orgreater and could be wrapped about a longitudinal axis of a hub 119 of areel 118, as shown in FIG. 11. Although only one position L.sub.2 isshown, it is recognized that there are a plurality of positions L.sub.2spaced along the length of the longitudinal axis L.sub.1 . Additionally,as shown in FIG. 14, the strip can also conform to twisting relative toits longitudinal axis L.sub.1 of up to 10 degrees per inch. The stripcan also bend to conform to localized heat sink surface flatnessvariations having a radius of at least 1 inch. FIG. 14 shows a layeredstructure 100 approximately 12 inches long twisted approximately 10degrees per inch. By conforming to variations in heat sink base materialshapes, heat transfer from the LED heat sink slug is greatly improvedover rigid board applications.

The layered structure 100 is pre-populated with a plurality of LEDs 125and other Surface Mount Technology (hereinafter “SMT”) electricalcomponents well known in the art for completion of a solid statelighting electrical circuit cable of producing light. An example of apre-populated layered structure could include the layered structure 100,a plurality of LEDs positioned longitudinally along the circuitapproximately every 1.6 inches, linear drivers positioned longitudinallybetween every sixth LED and seventh LED, and connectors for power placedlongitudinally approximately every 36 inches. An example of a suitableLED is 083A manufactured by Nichia Corporation of Detroit, Mich. Anexample of a suitable liner driver is NUD4001 manufactured by ONSemiconductor of Phoenix, Ariz.

FIG. 1 shows the layered structure 100 assembled and pre-populated witha plurality of LEDs and it is recognized that other SMT electricalcomponents and circuits well known in the art could also be included.The layered structure 100 is at least semi-flexible and can conform tomost curved, non-linear, and other irregular surfaces. Further, thelayered structure 100 may be cut to any desired length using an ordinaryscissors and cutting proximate the locations 120 indicated on the toplayer 101 and the locations 121 indicated on the bottom layer 112. Asshown in FIG. 6, a connector 122 is operatively connected to the layeredstructure to provide power to the LED system, and if it is desired toconnect two layered structures together, a board to board connector 123could be used. Such connectors are well known in the art.

Heat generated proximate the LED p-n junction is conducted from the LEDchip to the LED heat sink slug as designed by the LED manufacturer. TheLED heat sink slug typically is less than 0.25 inch in diameter or 0.050inch squared proximate the LED's base. When electrically driven, theheat generated by the LED 125 and transferred to the LED heat sink slugcan range from 1 to 5 Watts or more per 0.8 inch squared when applied toan adequate assembly heat sink. It is important to remove the heat awayfrom the LED p-n junction in order to maintain the manufactures'specifications for normal operation proximate the p-n junction.

The layered structure 100 provides a path for heat to be spread throughthe thin top layer 101 (copper 105), through the electrically insulatingintermediate layer 110, and into the bottom layer 112 (copper 113). Thebottom layer 112 provides a path for the heat to spread laterally andlongitudinally proximate over the top surface of the heat sink to whichthe layered structure 100 is operatively connected. The thermallyconductive adhesive layer 114 provides an interface layer which fillsthe voids between the bottom layer 112 and the mounting surface of theheat sink. Should there be any voids or air gaps in the mounting surfaceof the heat sink, the thermally conductive adhesive layer 114 fills inthe voids and air gaps up to 0.002 inch or less thus reducing the amountof voids and air gaps and increasing the amount of thermal transfer tothe heat sink. The layered structure 100 conforms to the heat sinkproviding the necessary thermal transfer capabilities necessary for highwattage LED s. Should it be desired to connect a layered structure toanother layered structure, a board to board connector 106 could be used.

The increased thermal performance of the layered structure 100 isachieved through four main aspects of the layered structure 100. First,the circuit design proximate the top surface of the top layer 101increases the amount of copper 105, or other suitable conductivematerial, with thermal conductivity of 400 Watts per meter per degreesKelvin (W/mK) at the LED heat sink slug providing for rapid spreading ofheat away from the LED 125. Second, the intermediate layer 110 provideselectrical isolation of the LED 125 for proper electrical functionalitywith breakdown voltage greater than 50 kV. Third, the circuit designproximate the bottom layer 112 increases the amount of copper 113 withthermal conductivity of 400 W/mK and overlaps the copper 105 of the toplayer 101 by the designed electrical circuit patterns to provide maximumheat transfer from the top layer 101, through the electrical isolationintermediate layer 110, and to the copper 113 of the bottom layer 112.Fourth, the thermally conductive adhesive layer 114 provides the finalheat transfer path to the assembly heat sink.

The resulting system, including the layered structure 100 mounted to theassembly heat sink with adhesive layer 114, has a thermal resistance ofless than 5 degrees Celsius per Watt (“° C./W”). This is compared tothermal resistances of greater than 5° C./W for flexible electricalsubstrates such as DuPont™ Kapton™ polyimide film. Rigid electricalsubstrates such as Metal Core Printed Circuit Boards (“MCPCBs”) as amaterial alone can achieve thermal resistances of less than 5° C./W, butsystems including MCPCBs have a thermal resistance much higher than 5°C./W due to deficiencies in thermal interface to the heat sink.Mechanical attachment of MCPCBs produces irregular pressures and pointcontact against heat sink surfaces. Additional materials could be usedto fill surface irregularities when using rigid electrical substrates,but these materials are limited to small gaps of 0.002 inch or less anddo not work well on curved surfaces having radiuses of 48 inches or lessproducing voids or air gaps of greater than 0.002 inch or surfaces withlocalized bends of radii.

The layered structure 100 could be used for many different applications.One application includes the production of light bars for retail displayfixtures, an example of which is shown in FIGS. 5 and 6 and anotherexample of which is shown in FIGS. 7 and 8. FIG. 7 shows a top layer 101with LED receptacles 104′ and driver locations 107′. Another applicationincludes the production of light bars for vertical refrigerationapplications, an example of which is shown in FIG. 9. These applicationsinclude extruded aluminum heat sinks 130, 140, and 150 onto which thepre-populated, at least semi-flexible layered structure 100 isconnected. The at least semi-flexible layered structure 100 is printedwith the electrical circuit design 103 as described above and thenpre-populated with LEDs 125 and other SMT electrical components asdesired. The pre-populated, at least semi-flexible layered structure 100is then either stored for later attachment to the heat sink or isimmediately applied to the heat sink.

Another example is shown in FIG. 10, which shows another embodiment ofthe present invention. An individual “peel and stick” LED and associatedcomponents could be positioned along a continuous strip of backing,which could be perforated, wound about a reel 118 as shown in FIG. 11,and removed individually from the backing. An example of a possible“peel and stick” strip including individual layered structures 100′along a strip of backing 115′ with perforations 116′ is shown in FIG.15. In FIG. 10, the heat sink to which the LED and associated components162 is a mounting surface 160 on a spot light. The individual assembliescould be used individually or connected to other individual assembles.Although only one LED is shown in FIG. 10, it is recognized that anydesired number of LEDs and associated components could be “peel andstick” from a continuous strip of backing.

Operatively connecting the pre-populated, at least semi-flexible layeredstructure 100 to the heat sink includes removing the layered structure100 from its storage container, paying out a desired length of thelayered structure from the reel and cutting the desired length (ifapplicable), removing the protective backing 115 (if applicable),placing the layered structure 100 onto a desired location on the heatsink, and applying pressure onto the layered structure 100 proximate thetop layer avoiding any sensitive electrical components (if applicable).Standard electro static discharge (“ESD”) precautions should befollowed. Direct pressure should not be applied to pressure sensitivedevices, such as LEDs with optical components. Manual pressure withone's finger(s) of approximately 2 pounds per square inch along 90% ormore of the layered structure should be sufficient for connection to theheat sink. A roller or other applicator device could also be used. Oncethe layered structure 100 is connected to a heat sink, the circuits areconnected to a termination board, which supplies power to the system asis well known in the art. If an adhesive layer is not used, the layeredstructure could be connected with thermal paste adhesive, thermal greasewith mechanical fastening, or other suitable securing means.

The layered structure is a low cost, at least semi-flexible structureconsisting in part of a very thin and flexible printed circuit substrateand a thermally conductive adhesive layer, which when operativelyconnected to a heat sink produces a superior thermal interface with theheat sink thus achieving overall superior system thermal performance.The circuit structure is designed in such a way as to allow the copperpads on the top layer to spread heat across the top surface. The thin,electrically insulating intermediate layer allows conduction of heatfrom the copper circuit area on the top surface to an even larger(nearly full coverage) copper on the bottom layer.

At least one high power LED is soldered onto the desired LED receptacleon the top surface of the layered structure. When electrical current ispassed through the circuit on the top surface of the top layer, the atleast one LED is energized and emits visible light. Based on the heatsink structure of the high power LED lamp, heat generated from theelectrical current passed through the LED is conducted to a heat sinkslug on the bottom of the LED. The efficiency of the LED andcorresponding light output performance is a direct function of thejunction temperature (“Tj”) of the LED with heat reducing the efficiencyof light production according to the manufacturer's specifications. Thelayered structure of the present invention works to rapidly spread heataway from the LED heat sink slug proximate the top surface andcorrespondingly rapidly conducts heat away from the top conductivecopper circuit layer, into the bottom electrically isolated copper area,into the heat sink, and into the surrounding air or structure.

The layered structure includes thermally conductive copper portionsproximate both the top and bottom layers, which are used to communicateheat flow through the less conductive intermediate layer, while at thesame time maintaining the at least semi-flexible properties of thelayered structure. The rapid spreading of heat away from the LEDs leadsto lower Tj values, higher light output, and higher componentreliability. Another benefit of an at least semi-flexible, layeredstructure is the further enhancement of thermal performance due to theability of the thin thermally conductive adhesive layer to conform toboth the copper portion of the bottom layer and the eventual heat sink.The ability of the at least semi-flexible, layered structure to conformto the eventual heat sink allows for improved intimate thermal contacton curved and less than perfectly flat heat sink surfaces.

Additional benefits of the at least semi-flexible, layered structure arethe utility and cost savings of building reeled, pre-populated, highwattage LED systems. Current reeled LED systems are available for lowerwattage LEDs (½ Watt or lower per 0.75 inch squared but do not exist forhigher wattage LEDs (greater than ½ Watt per 0.75 inch squared. The atleast semi-flexible, layered structure provides a substrate on whichsurface mounted, higher wattage LEDs can be mounted and then reeled ontoa 6 inches diameter or larger cored reel. Reeled continuous linearstrips of high wattage LEDs can be easily handled and applied to linearheat sinks during manufacturing assembly. Alternative methods withstandard circuit board materials require individual boards, whichrequire additional handling, labor, and packaging, adding cost andslowing production.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

We claim:
 1. A layered structure for use with a light emitting diodesystem, comprising: an electrically insulating intermediate layerdisposed between a top layer and a bottom layer; the top layer, theintermediate layer, and the bottom layer forming an at leastsemi-flexible elongate member having a longitudinal axis, the at leastsemi-flexible elongate member having sufficient flexibility to be bentalong the longitudinal axis to a radius of curvature of 6 inches; andthe top layer comprising electrical circuits and a protective coating;the top layer being pre-populated with electrical components, theelectrical components including at least one light emitting diode. 2.The layered structure of claim 1, wherein the bottom layer is 0.0007 to0.0056 inches thick.
 3. The layered structure of claim 1, wherein thetop layer includes 0.5 to 4.0 ounces per square foot of copper, theintermediate layer includes fiberglass 0.005 to 0.020 inch thick, andthe bottom layer includes 0.5 to 4.0 ounces per square foot of copper.4. The layered structure of claim 1, further comprising a thermallyconductive adhesive layer disposed under the bottom layer.
 5. Thelayered structure of claim 4, wherein the top, intermediate, bottom, andadhesive layers have a low thermal resistance.
 6. The layered structureof claim 5, wherein the top, intermediate, bottom, and adhesive layershave a thermal resistance of less than 5 degrees Celsius per Watt. 7.The layered structure of claim 1, wherein the layered structure is woundabout a hub of a reel.
 8. The layered structure of claim 1, theelectrical components including at least one light emitting diodegreater than 0.5 Watt per 0.75 inch squared.
 9. A layered structure foruse with a light emitting diode system, comprising: an electricallyinsulating intermediate layer interconnecting a top layer and a bottomlayer, the top layer comprising an electrically conductive material andthe bottom layer comprising an electrically conductive material; the toplayer, the intermediate layer, and the bottom layer forming an at leastsemi-flexible elongate member having a longitudinal axis, the at leastsemi-flexible elongate member having sufficient flexibility to be bentalong the longitudinal axis to a radius of curvature of 6 inches; andthe top layer being pre-populated with electrical components, theelectrical components including at least one light emitting diode. 10.The layered structure of claim 9, wherein the top layer includes 0.5 to4.0 ounces per square foot of copper, the intermediate layer includesfiberglass 0.005 to 0.020 inch thick, and the bottom layer includes 0.5to 4.0 ounces per square foot of copper.
 11. The layered structure ofclaim 9, further comprising a thermally conductive adhesive layerconnected to the bottom layer, the adhesive layer being configured andarranged to fill voids up to 0.002 inch.
 12. The layered structure ofclaim 11, wherein the top, intermediate, bottom, and adhesive layershave a low thermal resistance.
 13. The layered structure of claim 12,wherein the top, intermediate, bottom, and adhesive layers have athermal resistance of less than 5 degrees Celsius per Watt.
 14. Thelayered structure of claim 9, wherein the layered structure is woundabout a hub of a reel.
 15. The layered structure of claim 9, theelectrical components including at least one light emitting diodegreater than 0.5 Watt per 0.75 inch squared.